This invention relates to therapeutic devices incorporating water soluble glass compositions whose dissolution rate is strongly dependent on the pH of a surrounding aqueous medium.
Water-soluble glass compositions are finding a variety of uses in medical and veterinary applications for the controlled release of one or more active materials. There are special circumstances and particular types of product where it is desirable that the rate of solution of a glass should change rapidly when the pH of the aqueous medium is changed. For example, in some cases where a pharmaceutical product is to be delivered orally, e.g., as a tablet or bolus or as a granular material, it may be desirable that none should be delivered during the transport of the material from mouth to stomach but that the product should be delivered rapidly as soon as the product reaches the stomach.
A similar product arises when administering therapeutic materials, e.g., methionine, to ruminant animals. Many of these materials degrade under the alkaline conditions pertaining in the rumen and thus, with conventional delivery devices, very little material is delivered to the animal. This problem is further aggravated by the digestive process of a ruminant animal. Food is retained in the rumen for several hours, but the contents of the rumen are passed through the remainder of the digestive tract in a relatively short time.
An object of the present invention is to provide a delivery system that is inert under high pH conditions but becomes active under low pH conditions.